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From: spw2562@ritcv.UUCP (Fishhook)
Newsgroups: net.unix-wizards
Subject: Re: Prepending _ in C external names necessary?
Message-ID: <9113@ritcv.UUCP>
Date: Wed, 4-Dec-85 15:28:54 EST
Article-I.D.: ritcv.9113
Posted: Wed Dec  4 15:28:54 1985
Date-Received: Sat, 7-Dec-85 03:14:20 EST
References: <200@brl-tgr.ARPA> <174@altos86.UUCP>
Reply-To: spw2562@ritcv.UUCP (Fishhook)
Distribution: net
Organization: Rochester Institute of Technology, Rochester, NY
Lines: 47
Summary: _write or write?

[munch crunch]

I don't know if this is tru for all systems, but one system I worked
on passed parameters to system calls using specific registers.  Paremeters
to C functions are passed on the stack.  Therefore, for the compiler to
call user functions and system calls, it has to know what all the system
calls are.
UNLESS...
The system I worked on treated all system calls as function calls and
had function stubs which moved the stack parameters to the proper registers
then performed the actual system call.  Naturally, these stubs are written
in assembly.  For this to be possible, the system call has to be different
from the function call.  Answer?  Prepend every C function call with an
underline, prepend all the function stubs with an underline, DON'T prepend
system calls.  Therefore,

    ...
    write(fd,&data,bytes) in C becomes
    ...

      ...
      pushl fd,-@sp           or whatever, push the args to stack
      ...
      calls _write            and call the function
      ...

    And the library _write function stub is

      ...
    _write:                   address of function
      movl +@sp,d1            or whatever, move function args from
      ...                     stack to proper registers
      calls write             do the actual system call - no '_'
      ...                     and do the stuff to return the value it gets
                              from the system call

Without underscore prepending this would not be possible.

==============================================================================
        Steve Wall @ Rochester Institute of Technology
        USnail: 6675 Crosby Rd, Lockport, NY 14094, USA
        Usenet: ..!rochester!ritcv!spw2562 (Fishhook)   Unix 4.2 BSD
        BITNET: SPW2562@RITVAXC (Snoopy)                VAX/VMS 4.2
        Voice:  Yell "Hey Steve!"

    Disclaimer:  What I just said may or may not have anything to do
                 with what I was actually thinking...